Field of the Invention
This invention relates to water base lubricant compositions and more particularly relates to water base lubricant compositions which are low in foamability and are useful in a water soluble hydraulic fluid, a heat medium and a metal working fluid.
Heretofore, non-aqueous combustible lubricants whose bases are mineral oil or animal and plant oils, have been used for a hydraulic fluid, a heat medium, a metal working fluid and the like.
Recently, water base lubricants have been adopted in place of the non-aqueous combustible lubricants for the purpose of preventing fires which occur due to the leakage thereof and for the reason that when they are used for a metal working fluid, the treated lubricants are easily washed off from the metal surface.
As the water base lubricants, there are used, in general, water soluble compounds of high molecular weight for upgrading the lubricity and for increasing the viscosity thereof.
As the water base lubricants, there are known polyvinyl alcohol, salts of polymethacrylic acid, cellulose derivatives, polyoxyalkylene compounds and the like.
Especially, the polyoxyalkylene compounds have advantages in that they have low pour points for use as a synthetic lubricant, they are splendid in viscosity characteristics, they form a small quantity of sludge and varnish and they do not corrode sealing materials of all kinds such as metals, rubber and the like.
However, the known polyoxyalkylene compounds have disadvantages in that they are bad in oxidation stability at an elevated temperature, are apt to undergo thermal decomposition and are bad in lubricity because of their poor wetting on a metal surface, and they generate a large amount of foam.